Otitis media (OM) is one of the most common of childhood diseases throughout the world and the most common cause of hearing loss in children. Eighty percent of all children will have at least one episode of OM. Chronic OM, with effusion arises from a complex series of inflammatory events in the middle ear and affects approximately 5% to 30% of children. It can lead to inner ear pathology, acquired hearing loss and communication disorders. Bacteria are a common cause of OM. The widespread use of oral antibiotics has resulted in an alarming increase of antibiotic-resistant bacterial strains that cause OM, as well as other potentially fatal diseases including pneumonia and meningitis. An understanding of the role of bacterial components, inflammatory cells and mediators, and other molecules in middle and inner ear pathology may provide the foundation for new strategies in the treatment of OM, labyrinthitis, and OM-induced hearing loss. A multidisciplinary team of investigators in Minnesota with productive track records both in middle ear, round window membrane (RWM), and inner ear pathology has been recruited to tackle this important area of research applying basic science techniques (quantitative immunohistochemistry, morphometry, histopathology, biochemistry, molecular biology, and electrophysiology). The broad, long-term objective of this research is to determine how inflammation, biochemical changes, bacterial invasion and other factors associated with OM affect the structure and function of the RWM and inner ear. We plan to test the hypothesis that bacterial and inflammatory cells and their products alter protein expression, cell metabolism, and the structure of the RWM. These alternations allow the passage of bacterial components and inflammatory mediators through the RWM and into the inner ear leading to biochemical and structural changes in the inner ear, increased permeability of cells, and alternation of ion homeostasis, culminating in pathological conditions such as labyrinthitis and sensorineural hearing loss. Specifically, we will study the mechanism of molecular and bacterial permeability of the RWM, induced by OM, after innoculation of wild-type and isogenic mutant strains of Streptococcus pneumoniae (S. pneumoniae) or nontypeable Haemophilus influenzae (NTHi) into the middle ear and the influence of OM on structure, protein expression, ion homeostasis and auditory function of the inner ear. We will focus on the region of the cochlear lateral wall (spiral ligament and stria vascularis). This area of the inner ear is directly involved in the maintenance of ion and fluid homeostasis, which is crucial for the auditory mechanoelectrical transduction process in hair cells. Changes in expression of some proteins in the cochlear lateral wall alter ion homeostasis, which in turn may result in injury or death of various types of cochlear cells, especially hair cells, resulting in disturbance of auditory transduction and hearing impairment. We postulate that the information to be obtained from the proposed studies will bring new insight to identify specific therapeutic targets in OM and prevent sensorineural hearing loss due to OM. The following specific aims are designed to address these issues: 1) to study virulent factors involved in the permeability of S. pneumoniae and NTHi through the RWM and related pathological changes; and 2) to study the influence of bacterial OM on structure, protein expression, ion homeostasis and auditory function of the inner ear.